Mystic Brewery founder Bryan Greenhagen is pacing. It’s a recent Saturday, and with his new tap room in Chelsea having opened less than an hour ago, Greenhagen waits for a break in the chatter to shout out, almost apologetically, that he’ll be starting a tour soon. Mystic has been brewing beer since 2011, but this is the first time it’s had a dedicated sampling space.

Greenhagen did his post-doctoral research at MIT in fermentation science. He talks like a scientist, casually using the word “carotenoids” in a description of his last job. The company leases its Chelsea warehouse and brews beer off-site, at Pioneer Brewing in Sturbridge, then trucks the resulting “wort” back to Chelsea to ferment in big, square wine tanks.

Many of Mystic’s beers are aged in barrels, and all are bottle-conditioned, then placed in the controlled environment of an SUV tent in one corner of the warehouse. The entire process can take more than six weeks. In my duty as the writer of the Globe’s 99 Bottles beer column, I picked up a bottle of Descendent, an English-style beer brewed with Belgian yeast, at a South Boston liquor store last week. It had “batch No. 006” written on the label in black marker. It took a $300,000 investment to get the brewery up and running. Mystic brewed 300 barrels of beer last year.

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In its early years, founder Jim Koch sold Samuel Adams out of his car. Koch’s first goal was getting Boston Lager into 100 accounts in the city. When he reached the mark, he and a business partner celebrated by going to as many of those bars and restaurants as possible in one night and drinking a lager in each. His memory is hazy, but Koch says they made it to 23 before last call.

When Koch started out in 1984 there were trees growing out of windows in the site that would become his Jamaica Plain brewery. “Pablo the pornographic painter” was a neighboring tenant. Becoming the largest independent brewer in the country seemed like a long shot.

Last year, more than 2.7 million barrels of Samuel Adams were brewed, the most of any craft brewer.

The landscape Boston Beer grew from is vastly different from the one it inhabits today. With more than 2,300 craft breweries in operation around the country, Koch is no longer a tiny island in the middle of the vast ocean. Forty-four of those breweries, and counting, are in Massachusetts, including Greenhagen’s Mystic Brewery. Despite the proliferation, craft brewers still occupy just nine percent of the total US beer market.

To learn the state of the craft beer world, I sat down with Koch and Greenhagen in separate interviews. What follows are the edited and condensed highlights from those chats.

Q. Samuel Adams currently occupies about 1 percent of the market. Do you want to break into the 91 percent held by the major brewers like Anheuser-Busch and MillerCoors?

Dina Rudick/Globe Staff

Jim Koch is the founder of Boston Beer Co.

KOCH: No. Not at all. Never, ever been tempted to do that. My dad was a brewmaster. My grandfather worked for Anheuser-Busch. So I have a maybe more nuanced view of the big brewers. I don’t look down my nose at the big brewers. My dad told me this. He said, “Jim, remember. People don’t drink the market. They drink the beer.’’ So if you make a great-tasting beer, you’ll be OK.

The big guys make extraordinary amounts of beer that is clean, consistent, and inexpensive. I can’t do that as well. I can’t make Coors Light as well as Coors makes it. And their beers are perfectly designed to satisfy 90-something percent of the market. I’ve always known since the day I started that I was making beer for 5 percent of the market, maybe now it’s up to 10 percent. If I try to compete with the big guys, they’ll kill me.

Q. Does it bother you that most people still drink Bud and Miller Light? How do you view the big brewers?

GREENHAGEN: It doesn’t bother me at all, partly because I expect that they’ll continue to make the majority of the beer. They’re going to be around. They’re phenomenally informed and talented business people. They’ll probably be able to hold their own even with losing market share.

Q. What are the demographics of the folks who drink your beer?

GREENHAGEN: We definitely get a lot of the super enthusiasts, because we are sort of on that bleeding edge. We’re doing a native beer using yeast that we got from Massachusetts. Putting that in a package and putting it out there, it’s a little bit scary in a sense. Who’s going to grab that and not really know what we’re actually doing? It’s not a typical beer and it’s not really a Belgian beer, because it kind of tastes very wine-like and very different.

Dina Rudick/Globe Staff

Left: Mystic, the small local craft beer maker and right, Sam Adams, the big guy.

There’s a cultural movement, too, going away from big business. Every new restaurant that we see open is farm to table, wants our beer, wants to really express that local character.

Q. How do you feel about the big brewers competing with you and starting their own craft offshoots?

KOCH: [Long pause] You’ve got to accept the fact that we’ve created a beer culture and an excitement about beer that hasn’t existed in this country in 150 years. I’ve spent almost 30 years creating that. I can’t keep them out, I can’t expect them not to want their piece of it. I take it as a challenge. Just like they can make mass-produced, very pound-able light beer better than I can, I can make rich, flavorful, very high-quality craft beer better than they can.

I get excited about this stuff. To them it’s just another market segment. To me, it’s 30 years of my life, from starting in my kitchen. From dealing with decades of rejection and people thought I was crazy. So to me it’s not just a marketing term. To me it reflects passion and pride and authenticity that craft brewers have and the big guys, for all their virtues, don’t have.

GREENHAGEN: People are just so informed now. One of the reasons that’s less scary than it was is that the Internet just shines a light on everything. You can’t really hide where the beer comes from. Word of mouth is really what drives craft beer, maybe not big beer sales but craft beer sales.

The most important thing is trust. And that’s part of how the big brewers got big, because beer used to be very inconsistent. So if there’s doubt about the origins, about what the company says they do, it’s always been a problem, but the Internet just amplifies the speed that people get to know about that. If somebody’s interested in indigenous yeast, fermentation — maybe they’re making their own sauerkraut — they’re going to find us relatively quickly.

KOCH: Oh, all the time. At this point there’s so many new breweries that are often doing the same styles. So there’s not that much innovation in a standard IPA. There’s lots of slight variations of them. But if I see something interesting, I’m going to buy it. I was in New Jersey the last few days with our wholesaler. There were three or four times we went into a liquor store. We buy six-packs and sample them in the parking lot.

Q. How’s your relationship with the other local brewers?

GREENHAGEN: I would say it’s really good, from the ones who have been here for 20 years to brand-new ones. We kind of have to work together. We’re partially supporting each other by drinking each other’s beers.

We don’t have economies of scale on certain things. Barrels are a good example. We brought in a whole truckload of barrels from Napa and shared them with CBC, Hill Farmstead, Allagash, other local brewers. Harpoon got a few of them. Those are the kinds of things that we definitely have a common interest in.

Q. Is it hard competing against your friends?

GREENHAGEN: There’s so little beer you can make anyway that you’re not competing too much. You’re not pushing somebody off the shelf with three-year-old sour beer.

Q. What do you learn from trying different beer?

KOCH: Some breweries are more innovative than others. A lot of people start up a craft brewery today and make an IPA and a wheat beer and a porter or stout or something. And they’re not that much different. I’m not going to discover some great new way to make porter.

Q. How do you make your beer stand out without a marketing department?

GREENHAGEN: My perspective has sort of been, do something intrinsically interesting about the beer. We’ll be OK if we focus on what’s in the glass. That’s kind of where I’m coming from.

I think we have a lower threshold of the amount of beer we need to brew. This stuff is harder to make and you get a premium for that. There’s been a lot of strategy of trying to keep it all under control and not lose too much money early on. We’re closer. The tasting room is starting to help a lot. The idea is to sort of make a contribution to Massachusetts and Boston beer culture. You don’t want it to be entirely philanthropic, either.

Q. What are your biggest challenges?

GREENHAGEN: Not being medium-sized. Keeping up with the Internet is a challenge. We were caught off guard last year. You hit October and pumpkin beers come out, and you realize people buy a lot of pumpkin beer. That’s not something we really want to do, but next year we have to deal with the fact that people buy pumpkin beer like crazy. We have one delivery truck. If it gets a flat, what do you do? If somebody gets sick there’s nobody else. Our delivery department is one person, it’s my brother-in-law. If he can’t do it, I have to do it. Being really small you really don’t have that buffering.